1. Technical Field
The invention relates to a light-emitting device, and more particularly to a light-emitting device having a channel structure penetrated a semiconductor stack.
2. Reference to Related Application
This application claims the right of priority based on TW application Ser. No. 096126501, filed Jul. 19, 2007, entitled “LIGHT-EMITTING DEVICE”, and the contents of which are incorporated herein by reference.
3. Description of the Related Art
Light-emitting diodes (LEDs) are wildly used as light sources. Comparing with conventional incandescent lamps and fluorescent lamps, LEDs have advantages in power saving, longer life time and cost concern. LEDs replace conventional light sources and have been wildly used in various fields such as traffic lights, backlight modules, street lights and medical devices.
The demand of brightness for LEDs becomes higher as the application and development evolves. It is an important topic for the industry to improve the light efficiency and raise the brightness. One of the conventional methods is using substrate transfer process to replace the original growth substrate by a substrate that is transparent or thermally conductive. The light efficiency and brightness are therefore highly improved.
Referring to FIG. 9, a generally known InGaN light-emitting diode device manufactured by the conventional substrate transfer process is presented. The structure from bottom to top is followed by: a p-type electrode 41, a permanent substrate 42, a connecting layer 43, a semiconductor stack 44 (including a p-type semiconductor layer 443, a light-emitting layer 442 and an n-type semiconductor layer 441), an n-type ohmic contact layer 45 and an n-type electrode 46. The structure described above is a vertical structure formed by metal adhesion process. In order to have ohmic contact with the n-type electrode 46 and the n-type semiconductor layer 441, an un-doped layer (not shown in FIG. 1) under the n-type semiconductor layer 441 is removed, an n-type ohmic contact layer 45b is formed under the n-type semiconductor layer 441, and an n-type electrode 46 is formed on the ohmic contact layer 45. However, the removal of the un-doped layer from the structure usually causes a high driving voltage.